The present invention relates to image diagnosing apparatuses including radiographic apparatuses such as X-ray photographic apparatuses and X-ray CT (computed tomography) apparatuses and magnetic resonance imaging (MRI) apparatuses. It also relates to an image diagnosing method using such an image diagnosing apparatus.
An X-ray photographic apparatus, which takes X-ray photographs, is a type of non-destructive visual examination device which irradiates a subject with X-rays and visualizes the image shot mainly by printing it on a film to make the internal state of the subject known. And X-ray photographic apparatuses are put to practical use mainly in the field of medical care.
And in an X-ray CT apparatus, its scanning unit irradiates a subject with an X-ray beam while rotating an X-ray source around the subject, moves the subject in the direction of its body axis along with the rotation, and scans the volume of subject. Then, it generates images of sections of the subject on the basis of the data derived by the scanning. X-ray CT apparatuses are used for a wide range of purposes including medical uses and industrial uses.
Image diagnosing apparatuses, such as magnetic resonance imaging apparatuses, are known as apparatuses for shooting slice images of sections of a subject, and are used for a wide range of purposes including medical uses and industrial uses.
For instance, when a slice image is to be shot by using a magnetic resonance imaging apparatus, first a subject is accommodated in a space where a magnetostatic field is formed, and the spinning direction of protons in the subject, which is a living organism, is aligned with the direction of the magnetostatic field to achieve a state in which a magnetization vector is obtained. After that, the magnetization vector of the protons of the subject is varied by irradiating the subject with an electromagnetic wave of the resonance frequency from an RF coil and thereby generating a nuclear magnetic resonance phenomenon. And the magnetic resonance imaging apparatus receives with the RF coil magnetic resonance signals from the protons of the subject returning to the original magnetization vector, and generates a slice image on the basis of the received magnetic resonance signals (see Patent Document 1 for instance).
Every one of the image diagnosing apparatuses described above as examples including X-ray photographic apparatuses, X-ray CT apparatuses and magnetic resonance imaging apparatuses shoots images of the subject in an imaging space. The imaging space in this context means a prescribed area of the subject where X-rays irradiating the subject are transmitted in an X-ray photographic apparatus. In an X-ray CT apparatus, the imaging space means a prescribed area of the subject in which the scanning unit of the X-ray CT apparatus irradiates the subject with an X-ray beam while rotating the beam source around the subject and shifts in the direction of the body axis of the subject along with the rotation. In the magnetic resonance imaging apparatus, the imaging space means a prescribed area of the subject in which a slice image is generated on the basis of magnetic resonance signals received by the RF coil.
When an image of a subject is to be shot by using an image diagnosing apparatus, as the subject is always being moved by respiration or otherwise, the shot image may be blurred or suffer the generation of artifacts. Therefore, when taking an image of a subject with an image diagnosing apparatus, the operator tells the subject “Halt breathing” or “Inhale and then halt breathing”. Then, the subject temporarily halts his or her bodily motion by halting respiration in accordance with the operator's instruction, and the image is shot at the right timing.
Further, the image diagnosing apparatus may be provided with an auto-voice function to automatically issue a breathing halt instruction, such as “Halt breathing” or “Inhale and then halt breathing”, before shooting an image of the subject and to shoot after that instruction (vocal) thereby to catch the right timing of shooting. To further ensure the right timing of shooting, some X-ray CT apparatus, such as the one described in Patent Document 2, is provided with a respiration sensor which detects the subject's respiration either directly or indirectly, and shoots an image after the respiration sensor detects breathing halt after the breathing halt has been instructed.    [Patent Document 1] Japanese Unexamined Patent Publication No. 2002-165775    [Patent Document 2] Japanese Unexamined Patent Publication No. Hei 05 (1993)-056959
As the subject is enabled to halt his or her respiration in accordance with the breathing halt instruction by equipping an image diagnosing apparatus with an auto-voice function or having its operator giving an instruction directly to the subject, image shooting can be accomplished at the right timing.
Equipping the image diagnosing apparatus with an auto-voice function to give instructions to the subject uniformly determines the voice reproduction speed of the auto-voice function. Thus, the length of time from the start until the end of a voice message of the auto-voice function is fixed.
On the other hand, the timing of image shooting is not necessarily determined uniformly. For instance, when a contrast medium is administered to the subject before image shooting, there is a time lag until the administered contrast medium reaches the imaging space and the right timing of image shooting comes. And this time lag may vary in many ways with the positions of the subject or of the imaging space.
For this reason, the time lag and the length of time from the start until the end of the voice message may offer differ from each other, and even when the subject halts his or her respiration as instructed by the voice message, a lag may occur between the timing of the breathing halt and the timing of image shooting.
Furthermore, even if the length of time from the start until the end of the voice message of the auto-voice function is fixed, the subject may not be always able to halt his or her respiration exactly in accordance with the voice message. For instance, in response to the voice message “Inhale and then halt breathing”, some subject may hurriedly inhale and halt breathing while another may slowly inhale a long breadth and halt breathing. This would also invite a lag between the timing of breathing halt and the timing of image shooting. Especially where the subject is high-aged, his or her reaction to the reproducing speed of the voice message may be delayed, often making it difficult to respire in accordance with the voice message.